301 directory to its own index page

Hi all, long time member, first time poster.

I'm facing a peculiar situation. I just found my Google WMT tools 'Html Suggestions' showing a massive increase in duplicate page titles and meta descriotions (like 250 overnight). As far as I can tell, Google is suddenly treating EVERY directory and its index page as separate URLs.

e.g. http://www.example.com/directory/ and
http://www.example.com/directory/index.htm

are showing as dupes.

I know that technically they are unique URLs, but its never been an issue before AND all index pages have self referencing canonical tags. Just to make it clear, there is no page at /directory/. All my pages have actual page URLs like /directory/index.htm, /directory/page.htm, etc.

I'm guessing the way to handle this is to 301 all '/directory/' to the actual page (e.g. '/directory/index.htm')

I've tried creatng htaccess redirects like

Redirect 301 /directory/ http://www.example.com/directory/index.htm

and similar rewrite rules but end up either in an endless loop or getting a 403 forbidden error.

I know how to redirect a specific page like /directory/index.htm to /directory/, but can't get it to work the other way around.

Can anyone ofer an easy way to do this (or an alternative to 301 if that's not the best way to approach this? Just to be clear, I don't want to get into an SEO discussion over whether its better to redirect everything to the directory, I just want to deal with this flippin' Google mess and make sure all requests go to my actual pages!

Thanks very much for any suggestions!

EDIT: Drat! Almost forgot one of the most important bits. Not all pages use /index.htm. Some use /index.php and some use /page1.htm or similar (don't ask). So I don't think a site-wide htaccess or rewrite solution will work. I suspect I'll have to set up htaccess in each directory and specify what index url to redirect to from there.